The NFL asked a federal judge Monday to keep its lockout in place, saying there are no legal grounds to stop it while accusing the players of trying to manipulate the law with a bogus antitrust lawsuit.

The NFL filed its arguments in federal court in St. Paul, Minn., where U.S. District Judge Susan Richard Nelson has scheduled an April 6 hearing on the players' bid to stop the lockout.

The NFL said any decision on a lockout should wait until the National Labor Relations Board rules on an unfair labor practice charge against the now-dissolved union that contends the players failed to negotiate in good faith. The charge, filed Feb. 14, was amended March 11 to include reference to the union's decertification.

The NLRB said the case still is under investigation and had no further comment.

The legal salvo is just the latest in the fight between the league and players, who failed to forge a new collective bargaining agreement by March 11. That same day, Tom Brady, Drew Brees, Peyton Manning and six other current NFL players filed the antitrust suit and injunction request in federal court, and the NFL owners locked out the players, putting the 2011 season in jeopardy.

The NFL made three main points in Monday's filing. It said the injunction issue shouldn't be in federal court at all, the decertification of the union was a sham and the players' claim of "irreparable harm" has no merit.

Stopping the lockout, the NFL argued, would open all 32 teams to additional antitrust claims even for working together to solve the labor fight. Antitrust claims carry triple damages for any harm proven, meaning hundreds of millions of dollars are at stake.

In arguing that Congress has barred judges from halting lockouts, the league cited the Norris-LaGuardia Act -- Depression-era legislation passed with the intent of limiting employers' ability to crack down on unions, including their ability to seek court orders halting strikes. The NFL contends the law also protects an employer's right to impose a lockout in a labor dispute.

The league said the NFLPA dissolved eight hours before the labor agreement expired simply to avoid a six-month delay in filing its multimillion-dollar antitrust lawsuit -- a delay spelled out in the CBA.

Decertification, the league says, proved the players didn't want to negotiate in good faith and is a step used whenever it serves the union's purposes at the bargaining table.

The 57-page court filing includes statements from the players themselves that the league says backs its argument.

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"We decertified so that we could fight them from locking us out and go back to work," Indianapolis Colts center Jeff Saturday, NFLPA vice president, said the day after the March 11 decertification, according to the court filing. "And we feel like ... we can still negotiate this anytime you want."

According to the filing, NFLPA president Kevin Mawae said in a Sept. 29 interview that decertification was an "ace in our sleeve" that worked in the late 1980s in favor of the players.

"It's been a part of the union strategy since I've been in the league," Mawae said.

The league also cited comments from Baltimore Ravens wide receiver Derrick Mason nine days before the union was dissolved.

"So are we a union? Per se, no. But we're still going to act as if we are one," Mason, an NFLPA player representative, said March 2, according to the court filing.

The NFLPA didn't respond specifically to Monday's filing, but spokesman George Atallah said: "The NFL's actions don't match their words. They say they want a fair deal, but instead they locked out the players and now are trying to preserve that lockout through litigation."

NFL general counsel Jeff Pash said at the league's annual meeting in New Orleans that litigation will only delay the process of reaching a new CBA, and he repeatedly spoke of the importance of returning to the bargaining table. Pash said the league could re-initiate talks as soon as Wednesday if the players were so inclined.

"I guess one possibility which we have entertained would be going back into the mediation process," Pash said. "That has a confidential process, and it's one that we think had a lot of benefit over the course of about 18 days or so that we were in Washington with (federal mediator) George Cohen and his deputy. Perhaps that would be a way of re-starting."

In Monday's filing, the league accused the union of an illegal "heads I win, tails you lose" strategy, claiming the players want the NFL subject to antitrust claims "if it ceases or refuses to continue football operations" yet also "subject to antitrust liability if it does not" in a "flip of a switch" approach.

The players' antitrust suit -- known as Brady et al vs. National Football League et al -- attacked the league's policies on rookie salaries and free-agent restrictions such as franchise-player tags.

Peter Ruocco, the NFL's senior vice president of labor relations, wrote rebuttals to those contentions as part of Monday's court filing.

Ruocco argued that franchise tags are lucrative options for players, noting that Manning signed a multiyear contract worth nearly $100 million after being designated a franchise player in 2004.

As for the league-wide limit on rookie salaries, in which teams are permitted a certain pool to spend on players they draft, Ruocco noted that rookies last season, as a whole, signed contracts totaling $658.9 million in guarantees.

Ruocco also wrote that missing offseason workouts doesn't do "irreparable harm" to players, as they allege of the lockout. He noted that players work out on their own regardless.

NFL players would "undoubtedly argue" that free agency should begin promptly if the lockout were to be lifted, Ruocco added. That, he said, would create "considerable uncertainty" about the rights and abilities of teams wishing to re-sign their players and have a "detrimental effect" on the league's competitive balance.

That scenario would be "difficult, if not impossible, to unscramble the egg and return those players" to their original teams if the NFL were to win this case.